Specific\nAdsorption of Alkaline Cations Enhances CO–CO\nCoupling in CO<sub>2</sub> Electroreduction

Electrolyte\nalkaline cations can significantly modulate the reaction\nselectivity of electrochemical CO<sub>2</sub> reduction (eCO<sub>2</sub>R), enhancing the yield of the valuable multicarbon (C<sub>2+</sub>) chemical feedstocks. However, the mechanism underlying this cation\neffect on the C–C coupling remains unclear. Herein, by performing\nconstant-potential AIMD simulations, we studied the dynamic behavior\nof interfacial K<sup>+</sup> ions over Cu surfaces during C–C\ncoupling and the origin of the cation effect. We showed that the specific\nadsorption of K<sup>+</sup> readily occurs at the surface sites adjacent\nto the *CO intermediates on the Cu surfaces. Furthermore, this specific\nadsorption of K<sup>+</sup> during *CO–*CO coupling is more\nimportant than quasi-specific adsorption for enhancing coupling kinetics,\nreducing the coupling barriers by approximately 0.20 eV. Electronic\nstructure analysis revealed that charge redistribution occurs between\nthe specifically adsorbed K<sup>+</sup>, *CO, and Cu sites, and this\ncan account for the reduced barriers. In addition, we identified excellent\n*CO–*CO coupling selectivity on Cu(100) with K<sup>+</sup> ions.\nExperimental results show that suppressing surface K<sup>+</sup>-specific\nadsorption using the surfactant cetyltrimethylammonium bromide (CTAB)\nsignificantly decreases the Faradaic efficiency for C<sub>2</sub> products\nfrom 41.1% to 4.3%, consistent with our computational findings. This\nstudy provides crucial insights for improving the selectivity toward\nC<sub>2+</sub> products by rationally tuning interfacial cation adsorption\nduring eCO<sub>2</sub>R. Specifically, C–C coupling can be\nenhanced by promoting K<sup>+</sup>-specific adsorption, for example,\nby confining K<sup>+</sup> within a coated layer or using pulsed negative\npotentials.